316 C. A. Young on the Solar Corona. 



11474] 

 [C] 



Imve^,^ = Uk =^^^^^^y: and] 



to our last written equation we get a;— 09*4 a. 



Similarly, from Da, (7i=20), I find ^=^64 •5a; and from F, 

 (71=10) a:=lll-la. 



The last value is evidently too large, the discrepancy prob- 

 ably arising from the fact that Mr. Pye's instrument having a 

 prism of the extra dense and very yellow flint-glass considerably 

 reduced the intensity of the F line by absorption. 



Thus far, we have neglected the inequahties of shading and 

 " '■ ' ' both chromosphere and leucospher~ '^ 



crease m Dniiiancy pretty regularly from the limb of the sim, 

 and since the upper limit of the former is much the more defi- 

 nite, it is evident that the introduction of these considerations 

 would increase the computed ratio. We may, I think, then 

 safely assume that the angular area of the leucosphere is athast 70 

 times as great as the area of that portion of the chromospbere 

 and prominences which was exposed to view during the totabty. 

 I fear it is not possible to estimate this area with much certainty. 

 but think it could hardly have been equivalent to anytiiing less 

 than a ring of 9" or 10'' wide surrounding the sun. If so, we 

 find the leucosphere to be equivalent to a ring of about 10 m 

 width, and considering the irregularity of its outline, some oi 

 the angular prolongations would be likely to attain twice tbat 



l\am, of course, aware that the numerical data of this calcu- 

 lation are very uncertain, being mere estimates, not measure- 

 ments ; but the principle is correct, and the results are not 

 sensibly affected by any ordinary amount of atmospheric influ- 

 ence, since the different colored rays would not have the rafto 

 of their brilliancies much disturbed under any reasonably lair 

 conditions. 



The result agrees very well also with the photographs, draw- 

 ings, and estimates of skilled observers. 



As for the hng rays, both bright and dark, which are often^ 

 and perhaps usually, seen crossing the leucosphere and reachuii 

 far beyond, the question whether they are also solar appenclagt^ 

 appears to be very different and far more doubtful. . ^ 



In the first place, I doubt if they are always present - 

 any rate, in 1869, in a most exceptionally clear atmosptij;!^^' 

 I saw nothing of them at Burlington, Iowa, and believe r,^^ 

 am not absolutely certain) that none of our party did ; ^ 

 some observers in Kentucky saw them well, and at Sioux t . 

 they were especially conspicuous, as is evident from t^^ remarK 

 able, and I have no doubt, accurate picture given by Mr. 

 man in the Eclipse Report of the Naval Observatory. 



